The need to remove contaminating particles from semiconductor surfaces during the fabrication process has grown increasingly important as the size of semiconductor devices decreases. In an attempt to conquer this problem, manufacturers of semiconductors have employed two major techniques. A first group of manufacturers considers it impossible to remove particles once they attach to a surface, especially as the particles and level of integration reach submicron sizes. To solve the contamination problem, this group of manufacturers advocates taking preemptive actions to preclude contamination in the first place. A second group of manufacturers accepts the reality of contamination and advocates reducing contamination through the use of particle removal techniques.
Members of both groups currently use methods that suffer from serious deficiencies. As engineers continue to develop smaller, submicron-sized devices, the significance of submicron-sized contamination particles increases. For those in the first group of manufacturers, existing technology becomes less efficient as the contaminating particle size decreases. First, it becomes more and more difficult to design clean rooms and equipment that will prevent submicron-sized contamination particles from reaching the surface of a substrate. Second, existing techniques for characterizing contaminating particles are often ineffective for particles in the submicron range. Existing probes do not have a fine enough resolution to isolate contaminating particles of this size. Without an effective technique for characterization, manufacturers cannot identify the source of contamination. As a result, manufacturers have great difficulty eliminating these unknown contamination sources.
Those techniques used by members of the second group of manufacturers also have their failings. One popular technique employs brush scrubbing with water or isopropyl alcohol. This technique is ineffective even for micron-sized particles as it is nearly impossible to make a brush capable of reaching every micron of a surface even when used with a liquid.
Others in the second group of manufacturers advocate the use of high energy irradiation to remove particles. This controversial technique has not been proven effective and also risks damaging the substrate.
Members of the second group of manufacturers most commonly use a liquid surfactant solution for particle removal. When using this technique, a substrate is immersed in surfactant and the solution is normally agitated with a transducer operating at high frequencies. Liquid particle removal, however, suffers from several disadvantages. The efficiency of the technique decreases as the size of the contaminating particles decreases, making this process of decreasing importance for current and future generations of semiconductor processing. Current techniques are, at best, normally only effective for particles of micron size or larger. Liquid decontamination techniques are normally ineffective at the submicron level because the agitation created in the liquid frequently causes a boundary layer to develop on the surface with a thickness of approximately 0.2 to 0.3 microns. The boundary layer in the liquid prevents particles of this size, or smaller, from being affected by the turbulence created in the liquid. In addition, the liquids used for decontamination can actually cause contamination of the substrate. In particular, these liquids can leave both particulate and metallic contamination on the substrate. Chemicals also tend to be expensive to purchase and to dispose of.